Infrared (IR) sensors and associated infrared absorptive inks have traditionally been used for tracking and authenticating a number of different objects. More specifically, labels, barcodes, or other identifiable markings formed from infrared absorptive inks have been formed on the surface of a number of objects. Once marked, objects could then be illuminated with IR light and examined by an infrared sensor to authenticate or track the object.
While a number of methods for tracking and authenticating objects with infrared sensors and associated infrared absorptive inks have traditionally been used, these traditional methods have a number of limitations. Specifically, traditional IR dyes have associated visible color to them, causing the resulting dye-based IR inks and the printed matter to be visibly colored. Additionally, dye-based IR inks have traditionally suffered from limited solubility in an ink base and low light fastness and environmental fastness (air, water, humidity, and thermal fastness). Further, traditional pigmented IR absorptive inks typically included carbon black as the IR absorptive material, resulting in a dark and highly visible ink. Consequently, some of the tracking and authentication effectiveness of the IR absorptive ink may be compromised.